Recently, with an advancement of high speed, fine wiring pattern, and high density integration in semiconductor devices, there has been a request for decreasing a stray capacitance between wires and increasing a conductance of a wire to prohibit an increase of signal delay. A wire structure formed with a copper (Cu) wire having a low electrical resistance and an interlayer dielectric film of a low permittivity material, i.e., a low-k film has been widely used. In the era of a 45 nm half-pitch, a low-k film having a dielectric constant k of about 2.2 to 2.6 is required. Therefore, a porous low-k film having a lower dielectric constant has been considered as the low-l film.
The wire structure employing the low-k film and the copper wire is generally fabricated by means of a damascene method as follows. A photoresist film having a pattern corresponding to a wire pattern is first formed on the low-k film by means of a photolithography technology. Plasma etching is performed on the low-k film by using the photoresist film as a mask, thereby forming the wire pattern in the low-k film. The photoresist is then removed to leave grooves (trenches) or wire holes (vias) in the low-k film. The trenches or the vias are gap filled with wire metal, such as copper (Cu). A residual wire metal is removed by means of chemical mechanical polishing (CMP).
For the removal of the photoresist among the processes as described above, there has been employed a plasma ashing process including accomodating a substrate to be processed in a processing chamber maintained at a vacuum level, converting an oxygen-containing gas into a plasma while introducing the oxygen-containing gas, and ashing and removing the photoresist by using the plasma.
However, when ashing is performed by the plasma containing oxygen, there is a possibility that the low-k film may be damaged by oxygen radicals during the ashing process. If such damage occurs, an etching shape is damaged and the k value also rises, so that the effects of the low-k film are deteriorated.
Japanese Patent Laid-open Application No. 2006-049798 discloses a method of performing a silylation processing after ashing to recover such damage. The silylation processing reforms a surface of a damaged portion by using a silylizing agent so that an end group of the surface becomes an alkyl group such as a methyl group.
However, if ashing by using plasma of an oxygen-containing gas is performed for a long time, there is a problem in that the damage cannot be recovered sufficiently even though the silylation processing is performed.